Obesity is a major public health issue not only for the EU, USA, Japan but also for the world in general. It is associated with a number of serious diseases including diabetes, dyslipidemia, hypertension, cardiovascular and cerebrovascular diseases.
Although the underlying mechanisms are not yet fully understood, the impairment of insulin action in target tissues by accumulation of excess lipids is generally regarded as a key mechanism linking obesity to secondary pathologies (G. Wolf, Nutrition Reviews Vol. 66(10):597-600; D B Savage, K F Petersen, G1 Shulman, Physiol Rev. 2007; 87:507-520). Therefore, understanding of cellular lipid metabolism in insulin target tissues is crucial in order to elucidate the development of diseases associated with obesity.
A central event in lipid metabolism is the generation of malonyl-CoA via carboxylation of acetyl-CoA by the two mammalian ACC isoforms ACC1 (ACC-alpha, also termed ACCA) and ACC2 (ACC-beta, also designated ACCB) (D Saggerson, Annu Rev Nutr. 2008; 28:253-72). The malonyl-CoA generated is used for de novo fatty acid synthesis and acts as inhibitor of CPT-1, thereby regulating mitochondrial fatty acid oxidation. Furthermore, malonyl-CoA is also described to act centrally to control food intake, and may play an important role in controlling insulin secretion from the pancreas (G D Lopaschuk, J R Ussher, J S Jaswal. Pharmacol Rev. 2010; 62(2):237-64; D Saggerson Annu Rev Nutr. 2008; 28:253-72), further coordinating the regulation of intermediary metabolism.
Therefore ACC1 and ACC2 have been shown to be major regulators of fatty acid metabolism and are presently considered as an attractive target to regulate the human diseases of obesity, diabetes and cardiovascular complications (S J Wakil and L A Abu-Elheiga, J. Lipid Res. 2009. 50: S138-S143; L. Tong, H J Harwood Jr. Journal of Cellular Biochemistry 99:1476-1488, 2006).
As a result of its unique position in intermediary metabolism, inhibition of ACC offers the ability to inhibit de novo fatty acid production in lipogenic tissues (liver and adipose) while at the same time stimulating fatty acid oxidation in oxidative tissues (liver, heart, and skeletal muscle) and therefore offers an attractive modality for favorably affecting, in a concerted manner, a multitude of cardiovascular risk factors associated with obesity, diabetes, insulin resistance, nonalcoholic steatohepatitis (NASH) and the metabolic syndrome (L. Tong, H J Harwood Jr., Journal of Cellular Biochemistry 99:1476-1488, 2006; J W Corbett, J H Jr. Harwood, Recent Pat Cardiovasc Drug Discov. 2007 November; 2(3):162-80).
Furthermore recent data show that cellular toxicity mediated by lipids (lipotoxicity) is implicated in the susceptibitlity to diabetes associated nephropathy (for review see M Murea, B I Freedmann, J S Parks, P A Antinozzi, S C Elbein, L M Ma; Clin J Am Soc Nephrol. 2010; 5:2373-9). A large-scale genome-wide association study in japanese patients identified single nucleotide polymorphism in the ACC2 gene (ACACB) associated with diabetic nephropathy risk which was replicated in nine independent cohorts. In the kidney, dysregulation of fatty acid metabolism leading to increased fatty acid levels is believed to lead to glomerular and tubular dysfunction (M Murea, B I Freedmann, J S Parks, P A Antinozzi, S C Elbein, L M Ma; Clin J Am Soc Nephrol. 2010; 5:2373-9). Therefore inhibitors targeting ACC as key molecule involved in lipid oxidation have the potential to be beneficial for favorably affecting diabetic nephropathy.
Additionally, insulin resistance, deregulated lipid metabolism, lipotoxicity and increased intramuscular lipids have also been described to play a role in type 1 diabetes (I E Schauer, J K Snell-Bergeon, B C Bergman, D M Maahs, A Kretowski, R H Eckel, M Rewers Diabetes 2011; 60:306-14; P Ebeling, B Essén-Gustavsson, J A Tuominen and V A Koivisto Diabetologia 41: 111-115; K J Nadeau, J G Regensteiner, T A Bauer, M S Brown, J L Dorosz, A Hull, P Zeitler, B Draznin, J E B. Reusch J Clin Endocrinol Metab, 2010, 95:513-521). Therefore ACC inhibitors are also considered as interesting drugs for the treatment of type 1 diabetes.
In addition ACC inhibitors also have the potential to intervene in the progression of diseases that result from the rapid growth of malignant cells or invading organisms that are dependent on endogenous lipid synthesis to sustain their rapid proliferation. De novo lipogenesis is known to be required for growth of many tumor cells and ACC up-regulation has been recognized in multiple human cancers, promoting lipogenesis to meet the need of cancer cells for rapid growth and proliferation (C Wang, S Rajput, K Watabe, D F Liao, D Cao Front Biosci 2010; 2:515-26). This is further demonstrated in studies using ACC inhibitors which induced growth arrest and selective cytotoxicity in cancer cells and by RNA interference-mediated knock-down of ACC which inhibited growth and induced apoptosis in different types of cancer cells. Furthermore, ACC1 associates with and is regulated by the breast cancer susceptibility gene 1 (BRCA1). Commonly occurring BRCA1 mutations lead to ACC1 activation and breast cancer susceptibility (C Wang, S Rajput, K Watabe, D F Liao, D Cao Front Biosci 2010; 2:515-26)
Furthermore in central nervous system disorders including but not limited to Alzheimer's disease, Parkinson disease and epilepsy, impairments in neuronal energy metabolism have been described (Ogawa M, Fukuyama H, Ouchi Y, Yamauchi H, Kimura J, J Neurol Sci. 1996; 139(1):78-82). Interventions targeting this metabolic defect may prove beneficial to the patients. One promising intervention is therefore to provide the glucose-compromised neuronscerebral brain neurons with ketone bodies as an alternative substrate (ST Henderson Neurotherapeutics, 2008, 5:470-480; L C Costantini, L J Barr, J L Vogel, S T Henderson BMC Neurosci. 2008, 9 Suppl 2:S16; K W Barañano, A L Hartman. Curr Treat Options Neurol. 2008; 10:410-9). ACC inhibition leading to increased fatty acid oxidation may thereby result in increases in the blood levels of ketone bodies thereby providing an alternative energy substrate for the brain.
Preclinical and clinical evidence indicates that ketone bodies can provide neuroprotective effects in models of Parkinson's disease, AD, hypoxia, ischemia, amyotrophic lateral sclerosis and glioma (L C Costantini, L J Barr, J L Vogel, S T Henderson BMC Neurosci. 2008, 9 Suppl 2:S16) and improved cognitive scores in Alzheimers Diseases patients (M A Reger, S T Henderson, C Hale, B Cholerton, L D Baker, G S Watson, K Hydea, D Chapmana, S Craft Neurobiology of Aging 25 (2004) 311-314). The end result of increased ketone levels is an improvement in mitochondrial efficiency and reduction in the generation of reactive oxygen species (for reviews see L C Costantini, L J Barr, J L Vogel, S T Henderson BMC Neurosci. 2008, 9 Suppl 2:S16; K W Barañano, A L Hartman. Curr Treat Options Neurol. 2008; 10:410-9).
Furthermore, the potential of ACC inhibitors as antifungal agents and as antibacterial agents is well documented (L. Tong, H J Harwood Jr. Journal of Cellular Biochemistry 99:1476-1488, 2006). In addition, ACC inhibitors can be used to combat viral infections. It was discovered recently that viruses rely on the metabolic network of their cellular hosts to provide energy and building blocks for viral replication (Munger J, B D Bennett, A Parikh, X J Feng, J McArdle, H A Rabitz, T Shenk, J D Rabinowitz. Nat Biotechnol. 2008; 26:1179-86). A flux measurement approach to quantify changes in metabolic activity induced by human cytomegalovirus (HCMV) elucidated that infection with HCMV markedly changed fluxes through much of the central carbon metabolism, including glycolysis, tricarboxylic acid cycle and fatty acid biosynthesis. Pharmacological inhibition of fatty acid biosynthesis suppressed the replication of two divergent enveloped viruses (HCMV and influenza A) indicating that fatty acid synthesis is essential for the replication. These examples show that acetyl-CoA fluxes and de novo fatty acid biosynthesis are critical to viral survival and propagation as the newly synthesized fatty acids and phospholipids are important for formation of viral envelopes. Changing the metabolic flux influences the absolute quantity of phospholipid available, the chemical composition and physical properties of the envelope negatively affect viral growth and replication. Hence, ACC inhibitors acting on key enzymes in the fatty acid metabolism, have the potential to be antiviral drugs.